The present invention relates to a liquid crystal display device, and more particularly to an IPS mode (In-plane Switching mode) liquid crystal display device.
In the IPS mode liquid crystal display device, a pair of transparent substrates are arranged such that they face each other in an opposed manner by way of a liquid crystal and a pair of electrodes are formed in a spaced-apart manner from each other on a liquid-crystal-side pixel region of one transparent substrate and an electric field is generated between these electrodes so as to control the light transmittance of the liquid crystal against the light which passes between these electrodes.
That is, the pixel electrode and the counter electrode are formed in the region surrounded by signal lines and the electric field which is parallel to the transparent substrates is formed in the region defined between these electrodes.
Here, these electrodes are arranged such that the counter electrodes are disposed at both sides of the pixel region, that is, adjacent to the signal lines (drain lines), a pixel electrode is disposed adjacent to one of the counter electrodes, a counter electrode is disposed adjacent to this pixel electrode, another pixel electrode is disposed adjacent to this counter electrode and the other one of counter electrodes is disposed adjacent to this pixel electrode.
Such constitution is formed so as to prevent the electric field from the drain lines from terminating at the pixel electrode and to allow the electric field to terminate at the neighboring counter electrode thus preventing the invasion of noise.
On the other hand, on the other transparent substrate which is disposed such that it faces one transparent substrate in the opposed manner, a black matrix is formed thereon and this black matrix is formed so that it can shield not only the drain lines but also regions defined between the drain lines and the counter electrodes which are adjacent to these drain lines.
As mentioned previously, the electric fields are generated between the drain lines and the counter electrodes which are adjacent to the drain lines and the black matrix is provided for preventing a viewer from seeing the change of the light transmittance of the liquid crystal caused by the electric fields.
From this, it is recognized that the respective counter electrodes which are disposed adjacent to the drain lines are arranged such that a pair of sides thereof which face the aperture of the black matrix have portions thereof exposed.
Further, recently, the liquid crystal display device which forms a region where a pair of above-mentioned electrodes are bent respectively so as to differ the direction of the electric field generated between these electrodes has been proposed (see Japanese Laid-Open Patent Publication 148826/1998).
Such a constitution is called a multi-domain system and is capable of resolving the inconvenience caused by the visual angle dependence of the liquid crystal display panel that when the visual point is inclined obliquely relative to the main visual angle direction of the liquid crystal display panel, the reverse phenomenon of the luminance is induced.
However, when a slight misalignment (particularly, a misalignment in a direction which intersects the drain lines) occurs with respect to respective transparent substrates which are arranged such that they face each other in an opposed manner by way of the liquid crystal, there arises a case that the positional relationship between the black matrix and the respective counter electrodes cannot be achieved.
In such a case, out of these electrodes, one counter electrode is extended from the black matrix in an exposing direction in an excessive manner, while the other electrode is retracted in a direction to be completely shielded by the black matrix.
That is, corresponding to the misalignment of respective transparent substrates, the region of light which passes through the aperture of the black matrix is narrowed and hence, the inconvenience that the substantial lowering of the aperture rate is brought about.
The present invention has been made in view of the above and it is an object of the present invention to provide a liquid crystal display device which can prevent the lowering of the aperture rate irrespective of the presence of such misalignment of the substrates.
Further, with respect to the above-mentioned liquid crystal display device of the multi-domain system, a phenomenon that when the white display is made by using a so-called xe2x80x9cnormally blackxe2x80x9d as the liquid crystal, the bent portions out of a pair of the electrodes become dark, or alternatively, when the device is darkened by using xe2x80x9cnormally whitexe2x80x9d, the bent portions become bright.
The former phenomenon brings about the lowering of the transmittance of light and the latter phenomenon brings about the lowering of the contrast so that both of them are not preferable and hence, their review is requested.
The present invention has been made in view of the above and it is an object of the present invention to provide a liquid crystal display device which does not bring about the lowering of the transmittance of light or the lowering of contrast.
Further, with respect to the IPS mode liquid crystal display device, the orientation films which are respectively formed on the transparent substrates arranged such that they face in an opposed manner by way of the liquid crystal can make their rubbing directions (initial orientation directions of the liquid crystal) directed in the same direction and the respective directions of the electric fields are respectively set to proper directions based on the initial orientation directions of this liquid crystal.
As a specific example, the liquid crystal display device where the initial orientation directions of the liquid crystal are set in parallel with the drain lines which supply video signals to respective pixels so that the pixel electrodes of the pixel region and the counter electrodes arranged in parallel with the pixel electrodes are formed such that they extend in a direction of drain lines in a zigzag pattern is known.
Among the inventions disclosed in the present application, the typical invention is briefly summarized as follows.
That is, the typical invention is characterized by the liquid crystal display device which includes a black matrix and respective electrodes which are respectively formed along opposing sides of an aperture portion of this black matrix, wherein respective electrodes are formed into a pattern where the light transmission region within the aperture portion of the black matrix becomes almost constant irrespective of the misalignment of the black matrix in a widthwise direction of the electrodes.
Further, among other inventions disclosed in the present application, the typical invention is briefly summarized as follows.
That is, the invention is characterized by the liquid crystal display device which includes an electric field generating region which generates an electric field parallel to a substrate and this electric field generating region has regions which respectively differ in the direction of electric field and the field intensity of a boundary portion between these respective regions is substantially made equal to the field intensity of respective regions.
In the liquid crystal display device having such a constitution, even when the electric field generating region extends while having the bent portions, the electric field of substantially equal intensity can be generated throughout the entire portions.
Accordingly, when the white display is performed by using a so-called xe2x80x9cnormally blackxe2x80x9d as the liquid crystal, it does induce the lowering of the transmittance of light or when it is darkened by using a so-called xe2x80x9cnormally whitexe2x80x9d, it does not induce the lowering of the contrast.
Further, among other inventions disclosed in this application, the typical invention is briefly summarized as follows.
That is, the light transmittance of the liquid crystal is controlled by the electric field generated in parallel with the substrates and the electric field has two kinds of directions and the initial orientation direction of the liquid crystal has a given angle with respect to signal lines which supply signals to electrodes which generate the electric field.
The liquid crystal display device having such a constitution is of a multi-domain system where the initial orientation direction of the liquid crystal has a given angle with respect to signal lines.
Accordingly, even when the rubbing treatment along the initial orientation direction is applied to the orientation film, the roller travels in an oblique direction relative to the signal lines.
This prevents the roller from coming into contact with the signal lines (an insulation film may be interposed) at one time so that the breakdown of switching elements such as thin film transistors caused by the invasion of the static electricity which is generated by the roller can be prevented.
Further, at the time of performing the rubbing treatment by way of a mask, the roller travels while having an angle relative to sides of the aperture of the mask, that is, the roller travels from one corner portion to the other corner portion of the aperture which face each other in an opposed manner and hence, the peeling-off at the sides of the aperture of the mask can be restricted.